Alexander W. Blayney

Vibro-Acoustic Modelling of the Outer and Middle Ear Using the Finite-Element Method

In this study, a computer-based method called finite-element analysis is used to predict the forced-frequency response of the ear, with and without an ossicular replacement prosthesis (PORP 0362, Xomed Surgical Products). The method allows visualisation of the dynamical behaviour of the tympanic membrane (TM) and of the ossicles. The finite-element model is fully three-dimensional and includes both ligaments and muscles, and accounts for damping caused by the TM, ligaments, incudostapedial joint and the fluids of the inner ear. For validation, comparison is made with experimental measurements of umbo displacement taken from the literature. The translation and rotation (both anterior-posterior and inferior-superior) of the stapedial footplate are investigated. It is predicted that the translatory motion of the footplate decreases with increasing frequency, except when the frequency of the acoustic signal matches the natural frequencies of the ossicular chain or outer ear canal. The tilting motion of the stapedial footplate is also predicted to depend on frequency of excitation. The presence of a prosthesis changes the dynamical response considerably by shifting the natural frequencies of the ossicular chain. Ratios of stapes motion with and without the prostheses are plotted as a function of frequency allowing this effect to be clearly observed.

The effect of prosthesis design on vibration of the reconstructed ossicular chain: a comparative finite element analysis of four prostheses.

Hypothesis It was hypothesized that the differences in the bioacoustic performance of ossicular replacement prosthesis designs, and insertion positions, could be quantified using finite element analysis. Background Many designs of prosthesis are available for middle ear surgery. The materials used, and the shape of the implants, differ widely. Advances in computer simulation technologies offer the possibility of replicating the in vivo behavior of the different prostheses. If this can be achieved, insight into the design attributes required for improved biofunctionality may be gained. Methods Micro-computed tomography and nuclear magnetic resonance imaging were used to obtain geometric information that was translated into a finite element model of the outer and middle ear. The forced frequency response across the hearing range of the normal middle ear was compared with the middle ear reconstructed with partial and total ossicular replacement prostheses. Results The amplitude of vibration of the footplate was more similar to that of the normal ear when a Kurz total ossicular replacement prosthesis was implanted than when a Xomed total ossicular replacement prosthesis was implanted. This may be attributed to the latters titanium link. Partial ossicular replacement prostheses were stiffest and had lower umbo vibrations and higher stapedial footplate vibrations. In all cases but one, the vibration of the prostheses had resonances that caused the vibration of the stapes footplate to be noticeably different from normal. Conclusion The authors confirmed the hypothesis that finite element modeling can be used to predict the differences in the response of ossicular replacement prostheses. This study shows that computer simulation can potentially be used to test or optimize the vibroacoustic characteristics of middle ear implants.

BENIGN NASAL SCHWANNOMA

Nerve sheath tumours of the head and neck region mainly involve the eighth cranial nerve with only 4 per cent occurring in the paranasal sinuses. Only 32 cases of benign schwannomas occurring in the paranasal sinuses have been reported. We present a further case, review the current literature, and discuss the clinical details and specific histological features.

A Dynamic and Harmonic Damped Finite Element Analysis Model of Stapedotomy

This study was undertaken in an attempt to better understand the mechanics of sound transmission at the footplate following stapedotomy. The insertion of a Teflon (polytetrafluoroethylene) stapes prosthesis introduces new constraints within the reconstructed ossicular chain which have an effect on the normal vibration patterns of the tympanic membrane. In a finite element model of the ear, constraints have been reproduced as a series of spring constants in the incus/prosthesis/footplate interfaces incorporating damping to simulate the impedance of the inner ear. At zero damping, the frequency response at the pseudo stapes footplate exhibit several maxima and minima between 800 Hz and 2.5 Hz. At higher damping values, these maxima and minima become smoothened out with two or three naturals occurring over the same frequency range. Severe ankylosis of a diseased footplate is reproduced by over-damped conditions. The umbo, incus and stapes footplate vibrate in phase with similar frequencies at light damping levels. The movement of the prosthesis at the pseudo-footplate can be large in the out of plane axis of the ossicular chain, unless sufficient support is provided at the reconstructed footplate. Clinically, this would suggest the vein graft interposed between the piston and stapedotomy hole should endow resistance and elasticity to the system.

Problems in Alloplastic Middle Ear Reconstruction

Alloplastic materials have been used in middle ear reconstruction since 1952. Biologically, biomaterials and specifically ceramics can be defined as being bioinert, bioactive or biodegradable; these terms being descriptive of the biochemical response provoked by the material in the host tissue. Various ceramics, carbons and polymers and their reactions have been studied by the author and his colleagues over the past 5 years utilising animal implantation and fibroblast culture studies aligned with experience from clinical usage. The qualities of the ideal alloplastic implant namely: biocompatibility, stabilisation and incorporation, the consistency of the implant and bioactive bonding and the biofunctionality or mechanics, are applied to the materials currently available. No single alloplastic material fulfills all criteria, the problems encountered in relation to the biomaterials are reported. A better understanding of the microstresses, fatigue and microfractures is necessary, before the ideal alloplastic biomaterial becomes available.

Cutaneous presentation of nasal lymphoma: A report of two cases

Two patients with nasal lymphoma were seen with cutaneous lesions. Multiple biopsy specimens, immunohistochemical techniques, and gene rearrangement studies were required to establish the diagnosis.

Nebulized racemic ephedrine in the treatment of acute exacerbations of laryngeal relapsing polychondritis

A case of relapsing polychondritis of the larynx and upper trachea is presented. We report the use of nebulized racemic ephedrine, as a new treatment modality of the life threatening airway oedema which characterizes acute exacerbations of this disease.

An experimental technique for determining middle ear impedance

A two-microphone technique was used to determine the middle ear impedance of a live subject. The procedure involved the application of standing wave tube theory and the assumption that the ear canal behaves like an homogeneous cylinder with plane acoustic wave propagation up to a certain frequency--2 kHz for the current analysis. During experimentation the subject lay on a bench with his head braced against a wooden fixture. Acoustic pressures were recorded from the ear canal by the use of a spectrum analyser and probe microphones with flexible tips. Resultant impedance curves show middle ear natural frequencies at 831 Hz and 1,970 Hz with high levels of damping. The reactive impedance curves show the influence of stiffness and ossicular mass on middle ear sound transmission. An advantage of the approach is that using features of the recorded data it is possible to calculate the effective probe tip to eardrum distance required for the calculation of the middle ear impedance. The two-microphone technique appears to be a promising tool for assessing healthy and diseased middle ear function.

Pulmonary embolism following tonsillectomy.

Acute post-operative pulmonary embolism is a serious potentially life-threatening complication which is not anticipated in young patients undergoing non-major surgery. We report a case in which a 32-year-old previously healthy woman developed a major pulmonary embolism following tonsillectomy. Subsequent investigations revealed the presence of an occult malignancy. This case highlights the role of paraneoplastic hypercoagulable states in the aetiology of venous thromboembolism and the importance of thromboprophylaxis in the presence of confirmed or suspected malignancy. To our knowledge no case of major pulmonary embolism occurring after tonsillectomy has been previously reported.